Many diseases associated with vascular disorders have few subjective symptoms. Organ dysfunctions are occasionally caused as symptoms become serious while patients are unaware thereof. In the case of heart disease, for example, such symptoms could directly lead to death. An example of an organ in which many blood vessels are present is the kidney. A blood vessel that has entered into the kidney branches into capillary blood vessels, and the resulting capillary blood vessels are coiled to form tissue referred to as a “glomerulus” having a spherical form. Metabolic products, extraneous materials, and the like that are not necessary for living organisms are filtered through the glomeruli and excreted into the urine in the end. The amount of blood transferred to the kidney is as much as approximately 200 ml every minute, and the amount of primitive urine filtered is said to be as much as 120 liters every day. The condition in which the blood vessels forming the glomeruli are damaged by various factors and 60% or more normal kidney functions are lost is referred to as kidney failure. When the remaining functions are 15% or more below the normal level, continuous dialysis treatment becomes necessary. Dialysis treatment requires a patient to visit a medical facility providing such treatment about 3 times a week, and each instance of dialysis treatment is provided by a specialist stuff over a period of 4 to 5 hours. Receiving dialysis treatment is equivalent to machine-dependent life maintenance, and it imposes serious economical hardship upon patients, in addition to significant lifestyle changes. Accordingly, delay of the initiation of dialysis is significant. It is said that as many as 250,000 patients receive dialysis treatment in Japan.
Japanese people have been familiar with high-salt foods, such as salt, soy sauce, and soybean paste, since ancient times. When excess salt intake surpasses the capacity of the kidney for salt elimination, the salt concentration in the body is elevated. As a result, the water content in the body is increased in order to reduce the salt concentration of the body fluid, which increases the vascular resistance, and sodium in salt stimulates the sympathetic nervous system or cell membrane to contract blood vessels. This imposes excessive burdens on blood vessels. If chronic stress imposed on blood vessels exhausts the heart or kidney and the organ becomes dysfunctional, organ transplantation or dialysis treatment becomes necessary when symptoms are serious. While a low-sodium diet is effective, low-salt foods are unbearable for Japanese people, who have been accustomed to salt since ancient times. In particular, elderly people with decreased taste sensitivity for salt may unfavorably continue to ingest excessive salt unawarely. Accordingly, many studies have heretofore been made regarding elimination of salt from the body, such as elimination from the body with the aid of Na—K exchange action utilizing dietary fiber.
In contrast, alginic acid is a polysaccharide with high viscosity contained in brown algae, such as Laminaria. Low-molecular-weight alginic acid resulting from degradation of alginate polysaccharide via heating under acidic conditions to result in a molecular weight of several tens of thousands to several hundreds of thousands is prepared in the form of sodium or potassium salt, and the resultant is used as a food additive in the form of a thickener. In general, it is considered that alginic acid is not absorbed by the intestinal tract, and it is reported that low-molecular-weight alginate is not absorbed by the small intestine and is not substantially digested by enteric bacteria in the large intestine (New Food Industry, 43, 2, 13-19, 2001). Salt of alginate polysaccharide or low-molecular weight alginic acid (e.g., potassium or calcium salt) is known to cause exchange of sodium ions and excretion of sodium ions from the body without absorption by the intestinal tract.
In addition, salt of alginate polysaccharide or that of low-molecular-weight alginate is treated with a Pseudoalteromonas microorganism or a processed product thereof to degrade such salt into an oligosaccharide. Patent applications have been filed for food products with high water solubility, low viscosity, and absorbability in the body that inhibit blood pressure elevation with the use of a salt of alginate oligosaccharide (JP Patent Publication (Kokai) No. 2002-272420 A), vascular endothelial growth accelerators (JP Patent Publication (Kokai) No. H11-43439 A (1999)), and preventive and therapeutic agents for circulatory diseases (JP Patent Publication (Kokai) No. H09-235234 A (1997)).